The invention relates to a method of grinding convex running faces and outside diameters on shaft-like workpieces in one set-up and a grinding machine for carrying out the method.
According to the prior art, the grinding of convex running faces and outside diameters on shaft-like workpieces is effected by means of angular plunge grinding machines, in which case the machining of the corresponding shaft parts has to be effected in a plurality of set-ups. This procedure is therefore based on a plurality of operations, since the shaft parts to be machined have to be ground repeatedly on various grinding machines. This involves repeated setting-up with further production disadvantages, for even the smallest dimensional and geometrical inaccuracies are transferred in a cumulative manner to the finished part from one set-up to the other set-up.
Against this background, the object of the invention is to provide a method of grinding convex running faces and outside diameters on shaft-like workpieces in one set-up. In particular, semielliptical or parabolic running faces are to be ground. Furthermore, a special machine, with which the disadvantages associated with the prior art are removed, is to be used for this purpose. In this case, the shaft parts to be machined are to be ground in one set-up with two CBN grinding wheels until the finished product is obtained. The method according to the invention is also to permit individual grinding operations on comparable workpieces by means of the special grinding machine.
This object is achieved by a method having the features as claimed in claim 1 and by a grinding machine as claimed in claim 6. The subclaims referring back thereto in each case develop the method technologically and the grinding machine in terms of design.
The method of grinding shaft parts having convex, in particular semielliptical or parabolic, running faces and desired, exact outside diameters on shaft-like workpieces is effected in one set-up on a pivotable grinding headstock. The grinding headstock comprises two arms which form an angle xcex1, which is in particular 60xc2x0, and at whose free ends grinding spindles are provided. A grinding wheel having at least one concave side face for producing a contour-conforming convex running face on the shaft part to be machined is mounted on the one grinding spindle, and a grinding wheel for producing exact outside diameters on the shaft parts to be machined is mounted on the other grinding spindle. The grinding of a shaft-like workpiece is effected in such a way that the workpiece, which has a plane-side section having a large diameter, is clamped between the centers of a work headstock and a tailstock and is supported with steadyrests at the bearing points of the workpiece.
To produce a running face which is convex, in particular semielliptical or parabolic, in cross section on the plane-side section of the shaft-like workpiece having a large diameter, a relatively large grinding wheel is used, and this grinding wheel, in cross section, has at least one concave, in particular semielliptical or parabolic, side face conforming to the contour of the running face, to be produced, of the shaft-like workpiece section.
According to one embodiment, the opposite side face of the grinding wheel is also of corresponding design if convex running faces are to be produced on both sides of the shaft-like workpiece section having a large diameter.
After the production of the convex running face or convex running faces, the grinding wheel of concave design in cross section is removed from the engagement region with the shaft-like workpiece section by pivoting the grinding headstock. At the same time, the second grinding wheel is set against the outer periphery of the shaft-like workpiece section by traversing the grinding headstock in the X-axis in order to grind an exact diameter.
If this shaft-like workpiece section having a large diameter is to be ground convexly, in particular semielliptically or parabolicly, on both sides, a grinding wheel having two concave, in particular semielliptical or parabolic, side faces which conform to the contour of the running faces, to be produced, of the shaft-like workpiece section having a large diameter is used from the beginning. In this case, after the production of the first convex running face of the shaft-like workpiece section having the large diameter, the grinding wheel is first of all moved on the X-axis out of the region of the shaft-like workpiece section having the large diameter and is pivoted against the previous pivoting direction of the grinding headstock. The workpiece is then moved by a feed movement on the Z-axis in the direction of the workpiece center axis in order to permit the infeed of the grinding wheel for producing the second convex, in particular semielliptical or parabolic, running face of the shaft-like workpiece section with regard to the X-axis. In the process, the second concave, in particular semielliptical or parabolic, side face of the first grinding wheel is brought into engagement with the other side face of the shaft-like workpiece section having the large diameter in order to produce the second convex running face there, which conforms to the contour of the second concave side face of the grinding wheel.
After the grinding of the one convex, in particular semielliptical or parabolic, running face and/or the grinding of the second opposite convex, in particular semielliptical or parabolic, running face of the shaft-like workpiece section having the large diameter, the grinding headstock is moved on the X-axis out of the region of the shaft-like workpiece section having the large diameter. A second grinding wheel, which is mounted on the grinding spindle of the other arm of the work headstock and forms an angle xcex1, which is preferably 60xc2x0, with regard to the arm having the spindle for the first grinding wheel, is fed in perpendicularly to the longitudinal axis of the shaft-like workpiece in order to produce the desired outside diameters on the corresponding sections of the shaft-like workpiece.
Suitable for carrying out the method is a special machine on whose machine bed a work headstock and a tailstock arranged in alignment in the longitudinal axis are arranged, the work headstock and the tailstock realizing the feed movement in accordance with the Z-axis. Furthermore, steadyrests which can be set against the bearing points of the workpiece are provided in this region of the machine bed. A two-armed grinding headstock is provided behind the arrangement of the work headstock and tailstock, each arm being equipped at the end with a grinding spindle for accommodating grinding wheels. The perpendiculars to the longitudinal axes of the two grinding spindles intersect in a plane at an angle xcex1 of preferably 60xc2x0 at the pivot axis of the two-armed common grinding headstock having the two grinding spindles arranged thereon at the end and carrying the grinding wheel. The grinding headstock is pivotable in a plane, preferably horizontally, and can be fed in along the X-axis vertically to the Z-axis.
This grinding machine permits the setting of optimum positions of use for the grinding wheels with regard to the workpiece to be machined. The arrangement of the two-armed grinding headstock having the grinding spindles attached in each case at the end for the first and second grinding wheels has the advantage that both grinding spindles are arranged on a common guide for performing the infeed movement in accordance with the X-axis. This arrangement ensures very high rigidity values, including the grinding carriage guide. The high rigidity of the grinding headstock and of the guide system on the guide carriage, due to the grinding in one set-up, produce high accuracy values on the end product produced by grinding. By contrast, the dimensional inaccuracies creeping in during a plurality of set-ups up to the production of the end product accumulate. The high rigidity values of the guide system therefore decisively improve the process reliability of the method and also bring about a reduction in the wear of the grinding wheels.